I need to know about cams.

[Coupe Devil]

Ok I am tired of not know what you guys are talking about when a cam question is rasied, Someone please explain duration and lift. Also what is the difference in sold lift and hydralci lift? I know this is a dumb question but I am still learning all this stuff.

Thanks
Brad

[Unit 5302]

Lift: The lift given is generally listed with the rocker ratio included. Rockers have a ratio of like 1.6:1 or 1.7:1 which increases the cam lift. Most cams are rated with 1.6:1 rockers for the Mustang.

Duration: 224*/224*@.500 means the exhaust valve is open for 224* of rotation at .500 lift. @.500 is the most common duration measurement cited. There is also say 282*/282* which would be overall duration.

Split Duration: means the intake duration and exhuast duration is different. Since most Ford heads are a little weak on the exhaust port, getting a split duration cam can make up for that by favoring the exhaust side. IE 220*/224*@.500

LSA: Lobe seperation angle. A wider lobe seperation angle indicates you'll retain more cylinder pressure. The smaller the lobe seperation angle, the less vacuum and cylinder pressure then engine will have.

Now, how they work.

If you have a long duration camshaft, the additional time the valves are open will increase the flow efficiently, but because of the greater duration, they will generally have a small LSA and when you get too big (at that point you'll have a race engine) the car won't want to idle and you'll have very poor vacuum forcing you to drop power brakes, etc.

Going high lift enables you to flow more without necessarily increasing duration. That means you can keep low end power/drivability while making more hp. The drawback to this is obvious. You're wasting a ton of hp lifting the valve way up. The more you lift, the stronger your valvetrain has to be, and the more friction and power drain you'll have.

Roller vs Non Roller: A roller cam/lifter uses a roller on the pushrod to decrease friction and pushrod side loads. With a non roller cam, a steep lift will be limited because you can potentially break parts.

Hydraulic vs Solid: A hydraulic lifter cam uses oil to assist the lifter in lifting the valves. They do not require adjustment like solid lifter cams, and because of that they are generally quieter (as long as you have oil pressure, hehe). They make for a smoother valvetrain, and ease the load on the valvetrain to make for a more efficient setup. The drawback is that at higher rpms the lifters have trouble "pumping up" or in other words, retaining oil in them keeping them from completely dropping down. That causes the valves to stay open longer and you lose your top end power because of the extreme loss of cylinder pressure. That generally takes place beyond about 7000rpms on a well put together engine. When you really rev a hydrualic engine, you need SERIOUS valve springs to force everything closed. Stock valvesprings/lifters can start to fail before redline when they are old.

Hope that helps a little.

[Jeff Chambers]

Not to nit-pick, but the durations are commonly given at 0.050" lifter movement, not .500".

Also, for roller cams, the roller is on the end of the lifter (not the pushrod) and rides on the cam lobe. Hydraulic roller lobe profiles can usually be more radical (higher ramp rates) than flat hydraulic profiles since the roller is better able to follow the profile. Solid flat & roller profiles can be even more radical yet since there is no pumping action associated with the lifter and they can be forced to follow a lobe with severe ramp rates by use of mondo spring pressures. For example, a high revving solid lifter cam may use spring pressures of 350# on the seat and more than 700# when open where your typical EFI hydraulic roller cam may only use 125# on the seat and 300# at full lift. Obviously, those high spring pressures of the solid cam don't come without some price.

[Coupe Devil]

Thanks guys. I did know what a roler cam was but was basically unsure about the rest of it. So I want to build a mild big block that I am more interested in living a long life that I am turning 8000. I know for a fact that a STOCK 460 crank and rod will turn 8000 but I have no need to turn that high of an rpm. What company makes a goord roller cam conversion or what do I need to make a roller car? I am having the block bored in the cam bearings to accept a larger roller bearing instead of just a standard brass bearing. I am using a set of Blue Thunder Cobra Jet heads and a Victor Intake. What cam size do you recommend. This is a drag car only, not for the street so idle really isnt a concern. I will also be using Harland Sharp Roller rockers.

Thanks guys.
Brad